Minimally invasive instrument set, devices, and related methods

ABSTRACT

Methods of applying a locking cap to a bone anchor assembly. The bone anchor assembly includes a bone anchor and an elongate rod. The bone anchor includes a body that defines a channel and has a tissue retractor coupled thereto that defines a partial pathway to the channel.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.15/202,959, filed Jul. 6, 2016, which is a continuation application ofU.S. application Ser. No. 13/965,764, filed Aug. 13, 2013, which is adivisional of U.S. application Ser. No. 12/766,393, filed Apr. 23, 2010,now U.S. Pat. No. 8,535,318 issued Sep. 17, 2013, the contents of eachof which are hereby incorporated by reference as if set forth in theirentirety herein.

BACKGROUND

Retractors provide a surgeon with an access portal or pathway to asurgical site, for example during spine surgeries such as discectomies,laminectomies, facectomies, interbody fusions, pedicle screw fixationand similar procedures. Traditional spine surgeries were conductedutilizing an open procedure resulting in a relatively large incision,disruption or resection of significant soft tissue and long recoverytimes for patients. Minimally invasive techniques have becomeincreasingly popular, particularly for spine surgeries, whereinrelatively small incisions and surgical pathways are utilized to performsurgical procedures on a patient, generally resulting in a smallerincision or several relatively small incisions, less retraction andresection of soft tissue and shorter recovery times for patients incomparison to open procedures. Minimally invasive procedures are, incertain circumstances, able to obtain comparable or improved long termsurgical outcomes in comparison to open procedures and may provide shortterm benefits including reduced post-operative pain, reduced use ofpost-operative narcotics, reduced tissue disruption, thereby permittingreduced scar tissue and potential benefits if a revision is necessary,reduced blood loss, accelerated recovery time, shorter hospital staysand cosmetically appealing smaller incisions. However, the smallerincision or incisions diminish the line-of-sight for a surgeon todirectly view a surgical site, because patient soft tissue often limitsa surgeon's ability to view the surgical site.

A common procedure in spine surgeries involves fixing screws to severalvertebra and securing the screws and vertebra relative to each otherwith a rod. Such spinal constructs are typically implanted by mountingenclosed or substantially enclosed cannulae or sleeves to the screwssuch that the enclosed cannulae or sleeves create a surgical pathwaythrough soft tissue and provide access for the surgeon to the surgicalsite. Minimally invasive spine instruments utilized for such procedurescan be difficult to assemble, limit a surgeons ability to view thesurgical site, are bulky and extend a significant distance out of apatient's skin, may detach from the screws during the procedure, arecomplicated to operate involving many steps, result in proceduresinvolving removal and replacement of multiple instruments, inhibitimaging utilizing a C-arm or Fluoroscope as a result of their size andmaterial composition and may be difficult to detach from the screws atthe conclusion of the procedure. In addition, current minimally invasivefixation of screws and placement of rods in spine surgery often resultin undesirable levels of trauma to a patient's soft tissue in and aroundthe surgical site, along the surgical pathway and proximate theincision. Once assembled for rod insertion, these conventional minimallyinvasive systems are typically locked into a predetermined position andinhibit a surgeon's options in adapting their surgical technique to aparticular patient's anatomy or in adapting the instruments to implantthe components in a manner that would benefit the patient.

Certain conventional, minimally invasive spine instrumentation for theplacement of pedicle screws and rods is bulky and complicated to utilizewith multiple tool exchanges and complicated steps in mounting,removing, aligning and otherwise manipulating the bulky instrumentationto secure screws in the vertebrae and fix the rod to the implantedscrews. A surgeon is often unable to directly visualize the surgicalsite, the screws and/or the rods once they are implanted in a patient,because of the bulky instruments and the relatively small size of thesurgical incisions. Accordingly, a surgeon often relies on fluoroscopyto verify that screws and rods are properly placed in a patient and aresecurely fixed together. Accurate intra-operative visualization of theimplant construct can be difficult for a spine surgeon to verify withfluoroscopy because the relatively bulky metallic instruments attachedto the construct are radio-opaque.

In addition, the complicated procedures and instrumentation utilizedwith certain minimally invasive spine surgeries often require removaland replacement of different instruments through the enclosed cannulasor sleeves, thereby fatiguing a surgeon and extending the time that apatient is in surgery and subjected to anesthesia. Further, complicatedprocedures and instrumentation can lead to surgical delays, particularlyfor newly trained or novice surgical staff and surgeons when decipheringthe complicated procedures and instrumentation. For example, certaincounter-torque tools have been specially designed to fit within or ontominimally invasive spinal cannulas or sleeves that may result in severaltool exchanges to tighten locking caps onto spinal rods. Further, thegrasping handle of the counter-torque tool of conventional minimallyinvasive spine surgical sets can impede the surgeons visibility orprevent the use of other instruments during the procedure. Further,locking caps are often introduced through and into the substantiallyenclosed sleeves or cannulae of conventional systems with a screwdriverthat must be removed from the sleeve or cannula several times during theprocedure to introduce instruments such as the counter-torque sleeve, adistractor, a compressor or similar instruments. The screwdrivertypically a self-retaining tip that has a limited ability to retain thelocking cap if the sides of the sleeve or cannula are impacted with thelocking cap, resulting in the locking cap becoming detached and fallinginto the incision, thereby requiring removal of the screwdriver andretrieval of the locking cap through the sleeve or cannula or throughone of the minimal incisions. Accordingly, it would be desirable toconstruct a minimally invasive spine instrument set with acounter-torque tool that is relatively easy to secure to a screw fortightening of a locking cap and is relatively easy to remove and replaceso that the instrument is only in the theatre when necessary fortightening purposes. It is also desirable to design and construct aninstrument set that permits insertion of the locking cap into aminimally invasive incision utilizing a more robust retaining featurethan the self-retaining tip of a screwdriver.

Further, conventional minimally invasive instrument sets often have anunwieldy number of excess protruding parts proximate the incision, oftenfor the purpose of fixing the retractor to the polyaxial bone screw,that can block the surgeon's view of the site. Such unwieldy partsseverely inhibit a surgeons ability to visualize the construct at thesurgical site and result in generally blind insertion and significantreliance on the instrumentation. Coupled with the metallic compositionand bulky size of the instruments, visualization of the construct maynot be possible until all of the instruments are removed from theconstruct and the incision at the conclusion of the procedure.Subsequently, if the finally implanted construct is not acceptable tothe surgeon, the bulky and unwieldy instruments may have to bereattached to the construct or the surgeon may need to repair theconstruct through an open procedure.

The conventional minimally invasive spine instruments are typicallybulky and unwieldy to react forces encountered by the relatively long,hollow sleeves or cannulae during final tightening of the locking capsto the pedicle screws. The hollow sleeves or cannulae are typicallybulky and stiff specifically at the distal end portions to rigidly holdthe arms of the pedicle screws in position during final tightening toprevent splaying of the pedicle screws under final tightening loads. Inaddition, the hollow sleeve or cannulae are bulky and unwieldy alongtheir length to prevent twisting, splaying or breakage during the finaltightening step. This metallic bulk attached to the construct limitsvisualization, as was described above.

BRIEF SUMMARY

It would be desirable to develop a minimally invasive spine instrumentset that is relatively simple, utilizes relatively small components thatimprove fluoroscopic visualization of the screws and rod when theinstruments are attached thereto and are relatively low-profile at theskin incision to permit maximum line-of-sight potential for the surgeon.It would also be desirable to construct a minimally invasive spineinstrument set with a counter-torque tool that is relatively easy tosecure to a screw for tightening of a locking cap and is relatively easyto remove and replace so that the instrument is only in the surgicaltheatre when necessary for tightening purposes. In addition, it isdesirable to design and construct an instrument set that permitsinsertion of the locking cap into a minimally invasive incisionutilizing a more robust retaining feature than the self-retaining tip ofa screwdriver. Further, it is desirable to design and construct a set ofminimally invasive instruments that enhances a surgeons line-of-sightduring the procedure or while mounted to the construct and permitsvisualization utilizing fluoroscopy while the instruments are mounted tothe construct. It is also desirable to construct a minimally invasivespine instrument set that maximizes visualization by reducing the bulkof the instruments without compromising strength during the finaltightening step and preventing splaying of the instruments or thepedicle screws. It is further desirable to design and construct a systemfor minimally invasive spine surgery that allows for simple coupling anddecoupling of a tissue retractor to and from the bone anchor or pediclescrew, eliminates excessive field-of-view blocking instrumentation,minimizes the incision, and limits splay and cross-threading whilereducing excess tool replacement, thereby simplifying the surgicalprocedure.

Briefly stated, an exemplary instrument set for use in minimallyinvasive spine surgery includes a polyaxial bone screw and a tissueretractor having distal and proximal end portions and a partial pathwayformed therebetween. The tissue retractor is removably couplable to thebone anchor and rotatably fixed to the bone anchor when coupled thereto.An instrument has distal and proximal end portions and a hollow cavityformed therebetween, and is removably couplable within the partialpathway of the tissue retractor and rotatably fixed to the tissueretractor when coupled thereto. A drive shaft has a diameter that isless than a diameter of the hollow cavity of the instrument and isrotatable with respect to the instrument when positioned therein. Acounter-torque handle has a gripping end portion and an interlock endportion. The interlock end portion includes an instrument interface thatis releasably positioned within the hollow cavity of the instrument atthe proximal end portion thereof and is rotatably fixed thereto in anassembled configuration. The interlock end portion also includes anopen-ended slot having a width that is greater than the diameter of thedrive shaft such that the counter-torque handle is movable to and fromthe assembled configuration while the drive shaft is within the hollowcavity.

Another exemplary embodiment of the instrument set for performingminimally invasive spine surgery includes a polyaxial bone screw and atissue retractor having a distal end portion configured to receive andremovably couple to the polyaxial bone screw, a proximal end portionopposite the distal end portion, and a partial pathway formed at thedistal end portion and extending toward the proximal end portion. Thedistal end portion of the tissue retractor includes a blocking ribprojecting into the partial pathway of the tissue retractor and havingan inner surface. An instrument has distal and proximal end portions anda hollow cavity formed therebetween. The instrument is received withinthe partial pathway of the tissue retractor in an assembledconfiguration such that the partial pathway of the tissue retractor andthe hollow cavity of the instrument are coaxially aligned. The distalend portion of the instrument includes a blocking tab that is receivedby the blocking rib of the tissue retractor in the assembledconfiguration. The blocking tab contacts the inner surface of theblocking rib in the presence of a force exerted by the bone screw on aninterior surface of the tissue retractor.

A further exemplary embodiment of an instrument set for performingminimally invasive spine surgery includes a polyaxial bone screw havinga body and a bone screw. The body has a rod channel with a rod receivingportion disposed proximate the bone screw and a threaded portiondistally located from the bone screw. A tissue retractor has a proximalend portion, a distal end portion, and a partial pathway extendinglongitudinally from the distal end portion toward the proximal endportion. The distal end portion is removably coupled to the body of thepolyaxial bone screw. A locking cap has a threaded portion. A cap guidehas a proximal end portion, a distal end portion, and a hollow cavityextending longitudinally therebetween. The locking cap is removablyinsertable into the hollow cavity of the cap guide and rotatable withrespect to the cap guide when positioned therein. The cap guide ispositioned within the partial pathway of the tissue retractor in theassembled configuration such that the partial pathway of the tissueretractor and the hollow cavity of the cap guide are coaxially alignedand the locking cap is coaxially aligned with the body of the polyaxialbone screw to permit mating of the threaded portion of the locking capwith the threaded portion of the body.

A still further exemplary embodiment of an instrument set for use inminimally invasive spine surgery includes a bone anchor having an outersurface with at least one recess. A tissue retractor is removablycoupled to the bone anchor in an assembled configuration and includes abody having a proximal end portion and a distal end portion defining alongitudinal axis therebetween, a partial pathway extendinglongitudinally between the proximal and the distal end portions, awindow accessing the partial pathway and formed in the body proximatethe proximal end portion, and at least one cutout slot in the bodyextending generally longitudinally along a portion of the body proximatethe distal end portion. The at least one cutout slot has proximal anddistal end portions. A resiliently movable arm is defined by the atleast one cutout slot, is movably attached to the body at the proximalend portion of the at least one cutout slot, and has an attachment tabprojecting generally transverse to the longitudinal axis adjacent thedistal end portion of the at least one cutout slot and a protrusionprojecting generally transverse to the longitudinal axis adjacent theproximal end portion of the at least one cutout slot. The at least onetab is positioned within the at least one recess when the bone anchorand tissue retractor are in the assembled configuration. A removal toolhas proximal and distal end portions and is received within the partialpathway of the tissue retractor in an engaged position. The removal toolincludes a body having a proximal end portion and a distal end portionand at least one protrusion extending from the removal tool bodyproximate the distal end portion. The at least one protrusion isconfigured to engage the corresponding protrusion of the resilientlymovable arm of the tissue retractor in the engaged position to cause thetab of the resiliently movable arm to be spaced apart from the recess ofthe bone anchor. A resilient tab is disposed proximate the proximal endportion of the removal tool body. The resilient tab has (1) a relaxedposition wherein when the tissue retractor and removal tool are in theengaged position, the resilient tab projects from the body of theremoval tool and is positioned within the window of the tissueretractor, rotatably fixing the tissue retractor and the removal tool topermit removal of the tissue retractor from the bone anchor, and (2) adepressed position wherein the resilient tab is depressed toward thebody of the removal tool to permit insertion or removal of the removaltool from the partial pathway of the tissue retractor.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

The foregoing summary, as well as the following detailed description ofthe device and method, will be better understood when read inconjunction with the appended drawings. For the purpose of illustratingthe device and method of the present application, there is shown in thedrawings exemplary embodiments. It should be understood, however, thatthe exemplary device and method are not limited to the precisearrangements and instrumentalities shown. In the drawings:

FIG. 1 is a top perspective view of a first exemplary embodiment of abone anchor assembly or polyaxial pedicle screw without a locking cap(See FIG. 11) for use with an exemplary embodiment of a minimallyinvasive instrument set;

FIG. 2 is a front elevational view of the bone anchor assembly orpolyaxial pedicle screw of FIG. 1;

FIG. 3 is a side perspective view of a tissue retractor in accordancewith the exemplary embodiment of the instrument set;

FIG. 4 is a side perspective view of the tissue retractor of FIG. 3 withresiliently movable arms thereof in a flexed position;

FIG. 5 is a side perspective view of the pedicle screw of FIG. 1 coupledto the tissue retractor of FIG. 3;

FIG. 6A is a right-side perspective view of a cap guide instrument inaccordance with the exemplary embodiment of the instrument set;

FIG. 6B is a left-side perspective view of the cap guide instrument ofFIG. 6A;

FIG. 7 is a top perspective view of a counter-torque handle inaccordance with the exemplary embodiment the instrument set;

FIG. 8 is a side perspective view of the pedicle screw of FIG. 1, thetissue retractor of FIG. 3, the cap guide instrument of FIG. 6A, thecounter-torque handle of FIG. 7, and a screwdriver in an assembled orworking configuration in accordance with the exemplary embodiment theinstrument set;

FIG. 9 is an enlarged cross-sectional view of the cap guide instrumentof FIG. 6A coupled to the tissue retractor of FIG. 3, taken along line9-9 of FIG. 8 with only portions of the cap guide instrument and tissueretractor shown for clarity;

FIG. 10A is a side perspective view of two tissue retractors of FIG. 3in a partially nested configuration;

FIG. 10B is a top perspective view of the two tissue retractors of FIG.11A;

FIG. 10C is a side perspective view of the two tissue retractors of FIG.3 and two bone anchors of FIG. 1 secured to adjacent vertebrae in asurgical procedure;

FIG. 11 is a greatly enlarged front elevational view of the exemplarylocking cap of the pedicle screw of FIG. 1 in accordance with theexemplary embodiment;

FIG. 12 is a front elevational view of a distractor in accordance withthe exemplary embodiment the instrument set with the locking cap of FIG.11 mounted therein;

FIG. 13 is front elevational view of a compressor in accordance with theexemplary embodiment the instrument set with the locking cap of FIG. 11mounted therein;

FIG. 14 is a side elevational view of pedicle screws of FIG. 1 andtissue retractors of FIG. 11 further including the distractor orcompressor of FIG. 12 or 13, a rod, and a screwdriver in accordance withthe exemplary instrument set arranged for a surgical procedure;

FIG. 15 is a greatly enlarged top plan view of a body of the polyaxialbone screw of FIG. 1 coupled to the tissue retractor of FIG. 3;

FIG. 16 is a side elevational view of one component of a two-piecetissue retractor for use with the exemplary embodiment of the instrumentset;

FIG. 17 is a side perspective view of the two-piece tissue retractor ofFIG. 16 coupled to the pedicle screw of FIG. 1;

FIG. 18 is a greatly enlarged bottom plan view of the cap guideinstrument of FIG. 6;

FIG. 19A is a side perspective view of a scissor persuader in accordancewith the exemplary embodiment of the instrument set;

FIG. 19B is a side perspective view of a threaded persuader inaccordance with the exemplary embodiment of the instrument set;

FIG. 20 is a side perspective view of a removal tool in accordance withthe exemplary embodiment of the instrument set;

FIG. 21A is a side perspective view of a screw holder in accordance withthe exemplary embodiment of the instrument set;

FIG. 21B is a side perspective view of the screw holder of FIG. 21A witha safety shield in an actuating position; and

FIG. 22 is a top perspective view of a cap tray for holding several ofthe locking caps of FIG. 11 in accordance with the exemplary embodimentof the instrument set.

DETAILED DESCRIPTION

Certain terminology is used in the following description for convenienceonly and is not limiting. The words “right,” “left,” “lower,” and“upper” designate directions in the drawings to which reference is made.The words “inwardly” or “distally” and “outwardly” or “proximally” referto directions toward and away from, respectively, the geometric centeror orientation of the exemplary instrument set and related partsthereof. The words, “anterior,” “posterior,” “superior,” “inferior,”“lateral,” “medial,” and related words and/or phrases designateexemplary positions and orientations in the human body to whichreference is made and are not meant to be limiting. The terminologyincludes the above-listed words, derivatives thereof and words ofsimilar import.

FIGS. 1, 2 and 11 show an exemplary bone anchor assembly, polyaxial bonescrew or polyaxial pedicle screw 100 for use with an exemplaryinstrument set for minimally invasive spine surgery includes a body 102,a locking cap or a bone screw cap 700 and a threaded portion or bonescrew 104. Although the figures and description of the presentapplication show and describe the exemplary polyaxial bone screw 100, itwill be apparent to one having ordinary skill in the art based upon areview of the present disclosure that the exemplary instrument set maybe modified and adapted to function with a monoaxial bone screw (notshown). The exemplary instrument set may also be adapted to operate andfunction with numerous styles of pedicle screws and is not limited tofunctioning with the exemplary pedicle screw 100.

The bone screw 104 includes a plurality of threads 106 for securing thepolyaxial pedicle screw 100 to a vertebra V (FIG. 14) of a patient. Thebody 102 is polyaxially mounted to the bone screw 104 such that the bonescrew 104 is rotatable and pivotable with respect to the body 102. Alocking collar or collet 101 is mounted within the body 102 and ispositioned between the body 102 and a head of the bone screw 104 in anassembled configuration. The locking collar 101 facilitates thepolyaxial movement of the bone screw 104 relative to the body 102 andlocking of the body 102 relative to the bone screw 104 in a lockedconfiguration. An example of a polyaxial bone screw 100 that may beutilized with the exemplary minimally invasive instrument set isdescribed in International Patent Application Publication No. WO2009/015100 (“WO 100”), titled, “Polyaxial Bone Fixation Element” andfiled, Jul. 21, 2009, which is incorporated herein by reference in itsentirety.

The polyaxial bone screw 100 is generally constructed of titanium or atitanium alloy, such as an alloy including Titanium, Aluminum andNiobium (TAN—TI-6Al-6Nb—ASTM F 1295) but may also be constructed ofstainless steel, other metallic alloy materials or nearly any strong,stiff, biocompatible material that is able to take on the general sizeand shape of the polyaxial bone screw 100 and withstand the normaloperating conditions of the polyaxial bone screw 100. The polyaxial bonescrew 100, particularly the bone screw 104, may be provided havingdifferent lengths and/or diameters to accommodate anatomical variationsand bone structure of specific patients. The bone screw 104 may becannulated (not shown) along a central longitudinal screw axis X-Xthereof for positioning and placement of the polyaxial bone screw 100over a Kirschner wire or guide wire (K wires) (not shown) for guidanceof the bone screw 104 to the site of implantation on the vertebra V.

The body 102 includes a generally U-shaped rod slot or channel 108defined by two arms 110. The collet 101 includes a rod saddle 101 a thatis aligned with the rod channel 108 in an assembled configuration andreceives and contacts a spinal rod R (FIG. 10C) in a lockedconfiguration. The rod channel 108 terminates proximate the collet 101in an assembled configuration to form a rod receiving portion 112 thatis sized to accommodate the rod R (FIG. 10C). Each arm 110 includes aninterior surface 110 a having a threaded portion 114 located distallyfrom the bone screw 104 in the assembled configuration. An outer surface110 b of each arm 110 typically includes a recess 116 therein.

Referring to FIGS. 1-5, 9 and 10A-10C, a tissue retractor 200 of theexemplary instrument set for minimally invasive spine surgery for usewith the bone anchor assembly 100 includes a body 201 with a distal endportion 202, a proximal end portion 204 and a longitudinal tissueretractor axis L-L extending between the distal and proximal endportions 202, 204. The body 201 includes first and second slots 218 a,218 b at the distal end portion 202 and first and second longitudinallyextending edges 224, 226 that define the second slot 218 b at the distalend portion 202. The longitudinally extending edges 224, 226 extendbetween the distal and proximal end portions 202, 204. The firstlongitudinally extending edge 224 is generally parallel with thelongitudinal tissue retractor axis L-L of the tissue retractor 200, butis not so limited and may extend in nearly any path or include changesin direction along its length to adapt the design of the tissueretractor 200 to particular applications. The second longitudinallyextending edge 226 is generally parallel with the longitudinal tissueretractor axis L-L at the distal end portion 202 and curves in ahelix-like shape from an inflection point 217 near the distal endportion 202 toward the proximal end portion 204 such that the tissueretractor 200 has less structure than an enclosed or substantiallyenclosed cannula or sleeve. In this manner, the tissue retractor 200 mayprovide a more forgiving line-of-sight to a surgeon at a skin incision Iand to limit material of the tissue retractor 200, particularly adjacentthe skin incision I. Limiting the amount of instrument grade stainlesssteel or other difficult to image material of the tissue retractor 200may not only provides improved line-of-sight for the surgeon, but mayalso reduce the amount of interference with imaging systems, such asfluoroscopy, when a surgeon images the spinal construct with the tissueretractor 200 mounted to the polyaxial bone screw 100. Further, reducingthe amount of material of the tissue retractor 200 that extends out ofthe skin incision I generally reduces the size of the skin incision I.

The body 201 is typically constructed of instrument grade stainlesssteel but may also be constructed of titanium, aluminum, metallicalloys, polymeric materials, composite materials or nearly anyrelatively stiff, strong, biocompatible material that is able to take onthe general shape of the tissue retractor 200 and withstand the normaloperating conditions of the tissue retractor 200. A partial pathway 206extends longitudinally between the distal and proximal end portions 202,204 and is defined by the first and second longitudinally extendingedges 224, 226 and an inner surface 201 a of the body 201. The partialpathway 206 is nearly completely exposed along a majority of the lengthof the tissue retractor 200 as a result of the helix-shape of the secondlongitudinally extending edge 226 such that the tissue retractor 200functions to retract tissue, as will be described in greater detailbelow.

The body 201 generally defines a perimeter about the longitudinal tissueretractor axis L-L. The body 201 includes a first portion 220 adjacentthe distal end portion 202 and a second portion 222 extendinglongitudinally from the proximal end portion 204 to the inflection point217. A terminal portion 204 a of the proximal end portion 204 has agenerally linear and slightly curved cross-section. The body 201 alsoincludes at least one, but typically two, cutout slots 208 extendinggenerally longitudinally along a portion of the body 201 proximate thedistal end portion 202. The two cutout slots 208 are disposed oppositeone another proximate the distal end portion 202. Each cutout slot 208includes a pair of proximal end portions 208 a and a distal end portion208 b. A resiliently movable arm 210 is defined by each cutout slot 208.The arm 210 is movably attached to the body 201 at the proximal endportions 208 a of the cutout slot 208, by a deflection area 211,although other configurations for attaching the arm 210 to the body 201may be utilized, such as a spring-biased hinge or alternate mechanismsthat permit the arm 210 to pivot or flex relative to the body 201. Thebody 201 also includes a window 230 near the proximal end portion 204that may be utilized to engage or removably couple the tissue retractor200 to various tool and/or instruments, as will be described in greaterdetail below.

The tissue retractor 200 is removably couplable to the polyaxial bonescrew 100 and is rotatably fixed to the polyaxial bone screw 100 whencoupled thereto in an assembled configuration (FIG. 5). A portion of theinner surface 201 a of the body 201 receives and contacts a portion ofthe outer surfaces 110 b of the arms 110 of the body 102 in theassembled configuration, thereby restricting movement of the body 102 ofthe polyaxial bone screw 100 relative to the tissue retractor 200 in aplane perpendicular to the longitudinal axis L. The tissue retractor 200also includes at least one and typically four screw engagement ribs 214(FIGS. 3-5 and 8) extending longitudinally and inwardly toward thelongitudinal tissue retractor axis L-L from the distal end portion 202,generally toward the partial pathway 206. The body 102 of the polyaxialbone screw 100 includes a corresponding number of complementary collargrooves 118 (FIGS. 1 and 2) extending longitudinally from a proximal endportion 102 a of the body 102. Each screw engagement rib 214 mates withone of the corresponding collar grooves 118 when the tissue retractor200 is coupled to the polyaxial bone screw 100 such that the distal endportion 202 surrounds and grasps the arms 110, thereby restrictingrotation of at least the body 102 about the longitudinal axis L.However, when the tissue retractor 200 is mounted to the body 102, thetissue retractor 200 and body 102 are pivotable and rotatable relativeto the bone screw 104, at least until the body 102 is locked relative tothe bone screw 104, as will be described in greater detail below.Engagement of the screw engagement ribs 214 with the collar grooves 118provide a relatively bulky thickness, particularly at bulked-up portions203, relative to the remainder of the body 201 such that the distal endportion 202 of the tissue retractor 200 and, particularly, the screwengagement ribs 214 are able to react final tightening forces resultingfrom final tightening of the locking cap 700 to the body 102, as will bedescribed in greater detail below.

The arm 210 of the tissue retractor 200 includes an attachment tab 212located adjacent to the distal end portion 208 b of the respectivecutout slot 208, which projects generally transverse to and inwardlytoward the longitudinal tissue retractor axis L-L. The arm 210 has arelaxed position (FIGS. 3 and 5), wherein, when the bone anchor assembly100 and the tissue retractor 200 are in the assembled configuration, theattachment tab 212 is positioned within the recess 116 of the body 102of the bone anchor assembly 100 (FIG. 5). Longitudinal movement of thebody 102 within the partial pathway 206 along the longitudinal tissueretractor axis L is thereby restricted when the tissue retractor 200 ismounted to the body 102. The arm 210 also has a flexed position (FIG.4), wherein the arm 210 is deflected outwardly from the tissue retractor200, thus spacing the attachment tab 212 from the recess 116 of the boneanchor assembly 100 to permit longitudinal removal of the tissueretractor 200 from the body 102 or to permit the attachment tab 212 tomove into the recess 116 without interfering or being blocked by alocking edge 117 of the body 102.

When the tissue retractor 200 is engaged to the body 102 with the screwengagement ribs 214 positioned within the collar grooves 118, fivedegrees of freedom of movement of the tissue retractor 200 are limitedrelative to the body 102 by the engagement of the engagement ribs 214with the collar grooves 118. Specifically, the tissue retractor 200 isgenerally limited in any rotational movement and any translationalmovement except for movement away from the body 102 along thelongitudinal tissue retractor axis L-L by engagement of the engagementribs 214 with the collar grooves 118. The engagement of the attachmenttab 212 with the recess 116 and/or locking edge 117 generally blocksmovement of the tissue retractor 200 along the longitudinal tissueretractor axis L-L away from the body 102 and the final potential degreeof freedom of movement of the tissue retractor 200 relative to the body102. The attachment tab 212 may be sized and configured such that noclamping force is applied by the attachment tab 212 to the sides of thebody 102 when the attachment tab 212 is positioned within the recess116, as the attachment tab 212 may be configured to block axial movementof the tissue retractor 200 away from the body 102 in the engagedposition, as opposed to any additional degrees of freedom. Accordingly,the attachment tab 212 may only block movement of the tissue retractor200 away from the body through interference between the attachment tab212 and the locking edge 117 of the recess 116.

The tissue retractor 200 also generally includes at least one retainingtab 216 proximate the distal end portion 202 of the body 201 thatprojects from the inner surface 201 a into the partial pathway 206. Theretaining tab 216 is typically positioned on the inner surface of themovable arm 210 proximally or above the attachment tab 212. However, theretaining tab 216 may be located elsewhere within the partial pathway206. When the bone anchor assembly 100 is coupled to the tissueretractor 200, the proximal end portion 102 a of the body 102 abuts theretaining tab 216 (FIG. 5), thereby preventing further movement of thebone anchor assembly 100 along the longitudinal axis L into the partialpathway 206.

The tissue retractor 200 also includes at least one, typically the firstand second slots 218 a, 218 b, formed at the distal end portion 202 thatextend longitudinally from the distal end portion 202 toward theproximal end portion 204. The first slot 218 a of the exemplaryembodiment does not extend the entire length of the tissue retractor 200and terminates at a closed end portion 219. When the polyaxial bonescrew 100 is coupled to the tissue retractor 200, the first and secondslots 218 a, 218 b are aligned with the rod channel 108 of the body 102.The second slot 218 b is defined in the first portion 220 of the body201 by the first and second longitudinally extending edges 224, 226 ofthe body 201 that are separated by a first predetermined distance D₁about the perimeter. In the second portion 222 of the body 201 betweenthe inflection point 217 and the proximal end portion 204, a distanceabout an imaginary perimeter between the first and second edges 224, 226increases along the longitudinal tissue retractor axis L-L from thefirst predetermined distance D₁ to a second predetermined distance D2 atthe proximal end portion 204 of the body 201. The first edge 224 isgenerally linear and remains at a relatively fixed position on theperimeter along the length of the second portion 222 while the secondedge 226 progressively moves farther away in a curvilinear or helix-likemanner along the length of the second portion 222 to create the greaterdistance D2 at or near the proximal end portion 204. For example, thetissue retractor 200 shown in FIGS. 3 and 4 exhibits the helical-likecut to the second edge 226, although other cuts, such as a linear slant,taper, curve, or the like may be used. Further, both the first andsecond edges 224, 226 may exhibit the helix-like shape withoutsignificantly impacting the function of the tissue retractor 200 of theexemplary instrument set.

Referring to FIGS. 3-5 and 10A-10C, as shown in use, the tissueretractor 200 may reduce the invasiveness of a surgical procedureperformed at a motion segment M including a superior and inferiorvertebrae V of a patient's spine. For example, in the exemplaryembodiment, two tissue retractors 200 having the partial pathways 206and the helix-like second edge 226 are mounted to polyaxial bone screws100 and are angled toward one another into a nested or partially nestedconfiguration (FIGS. 10A-10C), which may reduce the size of the skinincision I. Specifically, the relatively open proximal end portions 204of the tissue retractors 200 are able to nest at the skin incision Isuch that a relatively small skin incision I is required. Conventional,enclosed minimally invasive sleeves or cannulae require an incision thataccommodates at least twice the diameter of a single sleeve or cannulaas the cross-section of these conventional, enclosed minimally invasivesleeves or cannulae form at least a figure eight (8) at the skinincision level. In contrast, the skin incision I required to accommodatethe nested tissue retractors 200 may be less than a full diameter of oneof the tissue retractors 200, because in the nested configuration thetissue retractors 200 have an mirrored, arcuate-shape or eye-shape (FIG.10B). In addition, a patient's soft tissue T tends to bias the tissueretractors 200 toward the nested configuration. Further, the tissueretractors 200 may be separated from the nested configuration by thesurgeon or utilized in a similar manner to a retractor to spread theskin incision I or move the soft tissue T to change the position of theskin incision I to maximize the surgeon's line-of-site to specific areasof the surgical site or elements of the construct, as long as the bodies102 remain polyaxially rotatable relative to the bone screws 140.

The tissue retractors 200 typically have a height HT that is slightlygreater than a distance from the implanted polyaxial bone screw 100 atthe vertebra V to the skin incision I. Accordingly, the tissue retractor200 extends only slightly outside of the skin incision I which mayprovide an increased line-of-sight into a generally conical incision CIfor viewing the surgical site and the impacted motion segment M. Thetissue retractor 200 is also relatively simple to attach to thepolyaxial bone screw 100 utilizing a snap-on action, as was describedabove, and is a single piece of structure that attaches to the body 102for use by the surgeon in a similar manner to a retractor blade.

The generally conical incision CI can be made through the patient's softtissue T to provide access to the motion segment M. The generallyconical incision CI is made possible by the nesting of the tissueretractors 200 at their proximal end portions 204 as a result of thehelix-like second edges 226. The resulting nesting permits a relativelyoblong or eye-shaped single skin incision I (FIGS. 10B and 10C).Further, the tissue retractors 200 are generally sized to extend only aslight amount from the skin incision I to further limit structure andrelative clutter in the line-of-sight of the surgeon.

Two bone anchor assemblies 100 can be guided through the generallyconical incision CI via a K-wire (not shown) to the superior andinferior vertebrae V, respectively, and are screwed into the vertebraeV. The surgeon may create the conical incision CI by blunt dissectionusing their finger guided by the Longissimus and Multifidus muscles,which may lead the surgeon to the pedicles of the superior and inferiorvertebrae V. Referring specifically to FIGS. 10A-10C, the tissueretractors 200 may also be inserted through the generally conicalincision CI at the same time that the bone anchor assemblies 100 areinserted into the generally conical incision CI or may be subsequentlycoupled to the bone anchor assemblies 100 after mounting the bone anchorassemblies 100 to the vertebrae V. The bone anchor assemblies 100 may beinserted through the conical incision CI with our without the tissueretractors 200 mounted thereto, but the tissue retractors 200 aretypically mounted to the bone anchor assemblies 100 during insertioninto the generally conical incision CI. The rod R is inserted throughthe generally conical incision CI as the tissue retractors 200 retractor hold the patient's soft tissue T away from the rod R. The utilizationof the tissue retractors 200 mounted to the polyaxial bone screws 100permits the surgeon to pivot and rotate the proximal end portions 204 ofthe tissue retractors 200 into several different orientations andlocations to maximize the line-of-sight to the surgical site, as thesoft tissue T is somewhat elastic and pliable such that the skinincision I and conical incision CI may be manipulated or otherwise movedby the surgeon. Such manipulation of the incisions I, CI is typicallynot possible with conventional minimally invasive spine instrumentationwherein tubes, sleeves or cannulae are fixed together in a predeterminedarrangement, because the tubes, sleeves or cannulae extending from thepolyaxial bone screws are locked together, thereby preventingmanipulation of the location, size and/or orientation of the incision orincisions.

The incision utilized for the tissue retractors 200 of a one-levelsurgery utilizing the exemplary instrument set is typically referred toas a mini-open incision. The exemplary mini-open incision results in thesurgeon working through a single, generally conical incision CI with atleast two polyaxial bone screws 100 and the spinal rod R included in theconstruct. The skin incision I of the generally conical incision CI maybe utilized to mount one, two or additional level constructs into bothlateral pedicles through a single mini-open midline incision bymanipulating the incision I, CI over muscle planes on either side of themidline and dissecting to the motion segment M along muscle planes ofthe soft tissue T.

Referring to FIGS. 16 and 17, when a surgery is performed across atleast two motion segments M, first and second tissue retractors 300 a,300 b may be mounted to a central bone screw 100. In an assembledconfiguration, the first and second tissue retractors 300 a, 300 bdefine a two-piece tissue retractor 300 that may be used with thecentral or otherwise interiorly positioned bone screw 100. The first andsecond tissue retractors 300 a, 300 b are similar to the one-pieceretractor 200 described above. Like numerals have been used for likeelements, except the 300 series numerals have been used for the firstand second tissue retractors 300 a, 300 b. Accordingly, a completedescription of the individual tissue retractors 300 a, 300 b has beenomitted, with only the differences being described. In the exemplaryembodiment, the two-piece tissue retractor 300 includes the first tissueretractor 300 a and the second tissue retractor 300 b, each of which isremovably couplable to a respective one of the arms 110 of the body 102of the polyaxial bone screw 100. Each of the first and second tissueretractors 300 a, 300 b includes a body 301 with a distal end portion302 and a proximal end portion 304 defining the longitudinal axis L-Land a partial pathway 306 defined between the proximal and distal endportions 302, 304. When coupled to the polyaxial bone screw 100, thefirst and second tissue retractors 300 a, 300 b hold back soft tissue Tcreating a void 307 that permits insertion of the rod R into thepatient. The first and second tissue retractors 300 a, 300 b may beutilized individually with the bone screw 100, but utilizing the pair ofthe first and second tissue retractors 300 a, 300 b with the bone screw100 is utilized to define the void from the incision I to the bone screw100 to accommodate introduction of the rod R into the bone screw 100.

The first and second tissue retractors 300 a, 300 b each include aninner surface 301 a, a portion of which receives and typically contactsa portion of the outer surface 110 b of a respective one of the arms110, similar to the connection described above with respect to theone-piece tissue retractor 200. The inner surface 301 a may have acurvature to define the partial pathway 306. Similarly, each of thefirst and second tissue retractors 300 a, 300 b includes a resilientlymovable arm 310 defined by a cutout slot 308 of the body 301, screwengagement ribs 314, and a retaining tab 316, which function similarlyto corresponding portions of the one-piece tissue retractor 200, andwill not be described in further detail. When coupled to the polyaxialbone screw 100, the first and second tissue retractors 300 a, 300 b format least one rod channel 318 extending longitudinally from the distalend portions 302 to the proximal end portions 304. The rod channel 318of the assembled first and second tissue retractors 300 a, 300 b isaligned with the rod channel 108 in the assembled configuration.

Referring to FIGS. 3-6B, 8 and 9, an exemplary cap guide instrument 400includes a generally cylindrical sleeve 401 having a distal end portion402, a proximal end portion 404 and a generally cylindrical, hollowcavity 406 extending between the distal and proximal end portions 402,404 along a longitudinal guide axis G-G. The cap guide 400 is generallyconstructed of instrument grade stainless steel but may also beconstructed of titanium, aluminum, metallic alloys, polymeric materials,composite materials or nearly any relatively stiff, strong,biocompatible material that is able to take on the general shape of thecap guide 400 and withstand the normal operating conditions of the capguide 400. The cap guide 400 and any of the additional components of theexemplary instrument set may particularly be constructed of Aluminum, anAluminum alloy or a polymeric material, particularly if improved imagingcompatibility is desired.

The cap guide 400 is configured to be removably couplable to the tissueretractor 200 within the partial pathway 206 such that the partialpathway 206 and the hollow cavity 406 are coaxially aligned and thelongitudinal tissue retractor axis L-L and the longitudinal guide axisG-G are coaxial (FIG. 8). At least one slot 410 is formed at the distalend portion 402 of the cap guide 400 that extends generallylongitudinally along a portion thereof. The slots 410 are defined byarms 422 that extend distally from the sleeve 401. Each arm 422 includesan arched cavity 424 for contacting the rod R (FIG. 19) during insertionof the locking cap 700 and concurrent reduction of the rod R into therod slot 108 of the body 102. The slot 410 is aligned with one of theresiliently movable arms 210 when the cap guide 400 is coupled to thetissue retractor 200. The cap guide 400 is relatively stiff and strong,particularly when compared to the tissue retractor 200, to react loadsencountered by the cap guide 400 when final tightening the locking cap700 to the body 102. The relatively stiff and strong cap guide 400 isalso able to limit damage to other components of the exemplaryinstrument set, such as the tissue retractor 200, the body 102, thelocking cap 700 or any of the other components of the exemplaryinstrument set during final tightening by reacting the relatively highloads during final tightening. The greatest loads and stressesencountered by the cap guide 400 and the other components of theexemplary instrument set is during final tightening and the cap guide400 is constructed to withstand this loading condition to protect theother components of the exemplary instrument set, certain of which aredesigned to maximize a surgeons line-of-sight and subsequently havecomparatively lower stiffness and strength. Thus, the cap guide 400 isexpected to be present in the incisions I, CI during portions of theprocedure when the stiff, strong construction is required to react thefinal tightening forces rather than during those portions of theprocedure when increased visibility is more desirable than increasedstrength.

The cap guide 400 also includes two indicia 432 at the proximal endportion 404 that are in alignment with the arched cavities 424 at thedistal end portion 402. The indicias 432 provide a visual indication toa surgeon for aligning the arched cavities 424 with the rod R whileinserting the locking cap 700 into the body 102 and the cap guide 400into the partial pathway 206 to ensure that the arched cavities 424engage and urge the rod R into the U-shaped rod slot or channel 108 ofthe body 102. Visually aligning the arched cavities 424 with the rod Rduring surgery without the indicias 432 could be difficult for asurgeon, because the cap guide 400, the tissue retractor 200 and thepatients soft tissue T are typically blocking the surgeons line-of-sightto the surgical site in the minimally invasive procedure. The indicias432 also assist in aligning a saddle portion 704 of the locking cap 700with the rod R when the locking cap 700 is engaged with the cap guide400. A compressor 1100, a distractor 1000, a remover or removal tool1200, a holder 1300 or other similar instruments that are introducedinto the partial pathway 206 may include similar indicia at theirproximal end portions to assist a surgeon in properly aligning theinstruments with the construct at the surgical site.

The cap guide 400 further includes at least one, and typically four,blocking tabs 408 proximate the distal end portion 402. When coupled tothe tissue retractor 200, the blocking tabs 408 are received by at leastone, and typically four, blocking ribs 228 of the tissue retractor 200(FIG. 9). The blocking tabs 408 typically contact inner surfaces 228 aof the corresponding blocking ribs 228 in the presence of a forceexerted by the bone screw 100 on the inner surface 201 a of the tissueretractor 200. The blocking ribs 228 are generally positioned close tothe screw engagement ribs 214 in the relatively narrow bulky section atthe distal end portion 202 of the tissue retractor 200. Accordingly, anyfinal tightening forces reacted by the tissue retractor 200 flow fromthe body 102 through the screw engagement ribs 214, through a short ornarrow bulked-up portion 203 of the tissue retractor 200 at the distalend portion 202, through the blocking ribs 228 and directly into thestrong, stiff cylindrical sleeve 401 of the cap guide 400. Accordingly,the forces of final tightening are essentially shielded form therelatively thin tissue retractor 200 by immediately directing the forcesinto the cap guide 400 by transferring the forces through the shortbulked upon portion 203 of the tissue retractor 200 at the distal endportion 202. The cap guide 400 therefore limits splay of the body 102 ofthe polyaxial bone screw 100 and the tissue retractor 200 duringinsertion of the locking cap 700.

A gap may be defined between the blocking tabs 408 and the innersurfaces 228 a of the corresponding blocking ribs 228 (FIG. 9) toaccommodate sliding insertion of the cap guide 400 into the tissueretractor 200 by providing clearance for insertion of the blocking tabs408 into the gap between the blocking ribs 228 and the body 201 of thetissue retractor 200. The gap is relatively small to limit splay of thetissue retractor 200 and the body 102 when the assembly is subjected tofinal tightening forces.

A guide button 426 extends radially outwardly from a side of thecylindrical sleeve 401 proximate the distal end portion 402. The guidebutton 426 has a button width W_(B) that is slightly smaller than a slotwidth W_(S) (FIG. 4) of the second slot 218 b. The guide button 426 alsoincludes relatively smooth, arcuate corners 428, particularly on adistal end portion. When inserting the cap guide 400 into the partialpathway 206 of the tissue retractor 200, the guide button 426self-guides and orients the cap guide 400 into proper alignment with thetissue retractor 200. For example, if the cap guide 400 is introducedinto the partial pathway such that the guide button 424 initiallycontacts the second longitudinal, helix-shaped edge 226, the guidebutton 424 slides down the second helix-shaped edge 226 until the guidebutton 426 drops into the second slot 218 b. When the guide button 426is positioned in the second slot 218 b in the assembled configuration,the arched cavities 424 and the indicias 432 are aligned with the rod Rand the blocking tabs 408 are positioned between the blocking ribs 228and the body 201, generally at four locations, to limit splay of thetissue retractor 200 and the body 102. In addition, the guide button426, the arms 422 and the blocking tabs 408 may cooperate to secure thecap guide 400 relative to the tissue retractor 200 in five of sixdegrees of freedom, with the exception being the movement of the capguide 400 out of the partial pathway 206 along the longitudinal tissueretractor axis L-L away from the distal end portion 202 of the tissueretractor 200.

Anti-splay wings 440 extend radially outwardly from the sleeve 401 nearthe proximal end portion 404 and define a capture groove 442 between thesleeve 401 and a distal wing end portion 440 a. In the assembledconfiguration, when the cap guide 400 is positioned in the partialpathway 206 with the blocking tabs 408 located between the blocking ribs228 and the body 201, the terminal portion 204 a at the proximal endportion 204 of the tissue retractor 200 is positioned within the capturegroove 442 to limit outward splay of the proximal end portion 204 duringuse. The two anti-splay wings 440 may be utilized, for example, with thetwo-piece retractor 300 to engage the proximal end portions of the firstand second tissue retractors 300 a, 300 b, respectively.

The cap guide 400 also typically includes clearance windows 450 andcapture grooves 460 on either side near the proximal end portion 404.The clearance windows 450 and the capture grooves 460 are utilized withadditional instruments of the exemplary instrument set to manipulate oralign the cap guide 400 with other instruments, which will be describedin greater detail below.

Referring to FIGS. 8 and 11, a screwdriver 500 may be utilized with thepolyaxial bone screw 100, tissue retractor 200 and cap guide 400assembly for threadably securing the locking cap 700 (FIG. 12) onto thebody 102 of the polyaxial bone screw 100. The screwdriver 500 includes ahandle 502 and a drive shaft 504 extending therefrom. The drive shaft504 has a diameter that is less than a diameter of the hollow cavity 406within the cap guide 400. Accordingly, the drive shaft 504 is rotatablewith respect to the cap guide 400 when positioned therein. The driveshaft 504 has a terminal end portion (not shown) which is configured tomate with a drive feature 701 on top of the locking cap 700 in areleasable, rotatably fixed fashion.

Referring to FIGS. 6A-8, a counter-torque handle 600 has a gripping endportion 602 and an interlock end portion 604. The interlock end portion604 includes an instrument interface 606 that is releasably positionablewithin the hollow cavity 406 at the proximal end portion 404 (FIG. 6B).When inserted into the hollow cavity 406, the instrument interface 606,and consequently the counter-torque handle 600, are rotatably fixed withrespect to the cap guide 400. The instrument interface 606 includes agenerally smooth inner surface 606 a and at least one spline 606 b on anexternal surface that mates with a complementary spline 412 in thehollow cavity 406 at the proximal end portion 404 of the cap guide 400.The at least one spline 606 b and the complementary spline 412 may becomprised of an octagonal spline or a spline having eight sides that areconfigured to align the gripping end portion 602 with the indicias 432and the rod R, are positioned perpendicular to the indicias 432 and therod or are oriented at forty-five degrees (45°) relative to the indicias432 and the rod R. Accordingly, the surgeon may orient the gripping endportion 602 generally perpendicular to the surgeon, generally pointingaway from the surgeon, generally pointing toward the surgeon or orientedat forty-five degrees (45°) toward and/or away from the surgeon. Suchorientations permit the counter-torque handle 600 to be adaptable toleft and right handed surgeons, to grasping by assistants and/orgenerally for surgeon comfort. The surgeon may utilize these variousorientations for comfort or for an assistant to hold the counter-torquehandle 600. The spline 606 b and complementary spine 412 may also beconfigured to have nearly any number of sides that are divisible by four(4), for example, square splines such that the surgeon has at least fourorientations to position the counter-torque handle 600 relative to thecap guide 400 or other instrument.

The interlock end portion 604 further includes an open-ended slot 610having a width greater than the diameter of the drive shaft 504. Thedrive shaft 504 is therefore not only rotatable within the open-endedslot 610 of the counter-torque handle 600, but the counter-torque handle600 is insertable and removable from the cap guide 400 while the driveshaft 504 is within the hollow cavity 406 of the cap guide 400 and whilethe cap guide 400 is within the partial pathway 206 of the tissueretractor 200. Accordingly, insertion, tightening, and counter-torqueoperations of the locking cap 700 can be performed without excessiveremoval and replacement of instruments and the counter-torque handle 600can be engaged with the cap guide 400 when it is required for finaltightening. In addition, the solid engagement provided between thecounter-torque handle 600 and the body 102 of the polyaxial pediclescrew 100 is relatively stiff and strong because of the arrangement ofthe tissue retractor 200 and the cap guide 400 and their engagement witheach other and the body 102. Specifically, final tightening loads aregenerally shielded from the tissue retractor 200, except at thebulked-up portion 203 between the screw engagement ribs 214 and theblocking ribs 228 at the distal end portion 202 where the tissueretractor 200 includes extra strength and stiffness to react the load.Accordingly, the instrumentation necessary for final tightening,including the tissue retractor 200, the cap guide 400 and thecounter-torque handle 600, is positioned at least near the generallyconical incision CI during the final tightening procedure and may bequickly removed and adapted during alternate steps of the procedure. Thecap guide 400 is not specifically necessary for final tightening of theconstruct, as final tightening may also be performed with the distractor1000, the compressor 1100, a threaded persuader 1500 or other relatedinstrument that engages the body 102, receives the screwdriver 500 andcounter-torque handle 600 and is able to retain the locking cap 700.

The instrument interface 606 may also be configured such that the atleast one spline 606 b is defined in the inner surface 606 a forgrasping the complementary spline 412 on the external surface of the capguide 400 (not shown). Such a configuration permits the open-ended slot610 to accommodate quick engagement and release of the counter-torquehandle 600 with the cap guide 400 without removal of the screwdriver 500or other instruments from the incision I.

Referring now to FIG. 11, the locking cap 700 is typically constructedof titanium or a titanium alloy, such as an alloy including Titanium,Aluminum and Niobium (TAN—TI-6Al-6Nb—ASTM F 1295) but may also beconstructed of stainless steel, other metallic alloy materials or nearlyany strong, stiff, biocompatible material that is able to take on thegeneral size and shape of the locking cap 700 and withstand the normaloperating conditions of the locking cap 700. The locking cap 700includes a threaded portion 702 and the saddle 704 rotatably mounted tothe threaded portion 702. The saddle 704 is generally machined with apost (not shown) that mates with an axial hole (not shown) in thethreaded portion 702 and is rotatably secured thereto. The locking cap700 is generally shown in WO 100 and is not limited to constructionsincluding the saddle 704 and the threaded portion 702. For example, thelocking cap 700 may be comprised of nearly any style or variety oflocking cap that is known to those having ordinary skill in the art. Thethreaded portion 702 includes a plurality of threads 712 that mate withthe threaded portions 114 of the inner surfaces 110 a of the arms 110 ofthe body 102 in the polyaxial bone screw 100. The saddle portion 704includes two downwardly extending arms 706, 708 that form an archedcavity 710 therebetween. The saddle 704 includes a grooved surface 704 athat assists in securing the saddle 704 to the rod R in the implantedand locked position. The cavity 710 is sized and shaped tocomplementarily receive the rod R when the locking cap 700 is mounted inthe polyaxial bone screw 100.

Referring to FIGS. 6A, 6B, 11 and 18, the locking cap 700 is removablyinsertable into a distal end portion of the hollow cavity 406 of the capguide 400 and the saddle 704 is rotatable with respect to the cap guide400 and the threaded portion 702 when the locking cap 700 is secured tothe cap guide 700. To accommodate the locking cap 700, the exemplary capguide 400 includes a movable cap tab 414 (FIG. 18), located proximatethe distal end portion 402 of the cap guide 400 and projecting into thehollow cavity 406. The cap tab 414 is disposed at a distal end portion418 of a resiliently movable arm 416 of the cap guide 400 (FIG. 6). Themovable arm 416 is attached at a proximal end portion 420 thereof to thesleeve 401 of the cap guide 400. The cap tab 414 may alternatively becomprised of a portion of thread (not shown) that projects into thehollow cavity 406 to engage the threaded portion 702 of the locking cap700 and secure the locking cap 700 to the distal end portion 402 of thecap guide 400. Further, the cap guide 400 may include additionalalternative mechanisms to temporarily secure the locking cap 700 in thehollow cavity 406 of the cap guide 400, such as hook and loop material,adhesive materials, clamps, releasable fasteners or like mechanisms.

In the exemplary embodiment, the movable arm 416 is constructed of aspring steel material and is welded at a proximal peripheral edge 416 ato the cap guide 400. A gap 416 b is defined between the movable arm 416and the cap guide 400 at a distal periphery of the movable arm 416 suchthat the distal end portion 418 of the movable arm 416 may flex toreceive and release the locking cap 700 during insertion and removal ofthe locking cap 700, respectively, from the hollow cavity 406. Thelocking cap 700 is prevented from being over-inserted into the hollowcavity 406 by a narrowed portion 409 (FIG. 18) of the cap guide 400 thatextends radially inwardly into the hollow cavity 406 proximate thedistal end portion 402 and abuts a top surface 702 a of the locking cap700 to align a longitudinal cap axis C-C with the longitudinal guideaxis G-G of the cap guide 400. The cap tab 414 is received in threads712 of the threaded portion 702 of the locking cap 700 when the lockingcap 700 is inserted and secured in the hollow cavity 406 of the capguide 400 in the assembled configuration.

With the locking cap 700 in the hollow cavity 406 of the cap guide 400,the cap guide 400 is positioned within the tissue retractor 200 suchthat the partial pathway 206 and the hollow cavity 406 are coaxiallyaligned and the locking cap 700 is coaxially aligned with the body 102of the polyaxial bone screw 100. In this assembled configuration, thelongitudinal cap axis C-C is generally coaxial with the longitudinaltissue retractor axis L-L and the longitudinal guide axis G-G. Thisconfiguration permits mating of the threaded portion 702 of the lockingcap 700 with the threaded portions 114 of the body 102 withoutcross-threading or the like because the alignment of the cap guide 400and cap screw 700 automatically provides vertical alignment of thethreaded portion 702 of the locking cap 700 with the threaded portions114 of the body 102 when the cap guide 400 is properly locked inposition within the tissue retractor 200 (FIG. 8). The drive shaft 504of the screw driver 504 is also preferably coaxially aligned with thelongitudinal tissue retractor axis L-L, the longitudinal guide axis G-Gand the longitudinal cap axis C-C in this assembled configuration (FIG.8).

Referring to FIGS. 6A, 6B, 8 and 12-14, other instruments such as thecompressor 1100, the distractor 1000, the removal tool 1200, the holder1300 or the like may be used in conjunction with the exemplaryinstrument set that also limit splay, cross-threading, and otherunfavorable consequences of insertion and final tightening of thelocking cap 700 to lock the rod R in the polyaxial bone screw assembly100 and the bone screw 104 relative to the body 102. For example, thecompressor 1100 and/or the distractor 1000 have many similar structuralfeatures to that of the cap guide 400, particularly at their distal endportions to engage the tissue retractor 200 and the locking cap 700.Accordingly, like numerals have been used for like elements, except the1000 series numerals have been used to identify features of thedistractor 1000 and 1100 series numerals have been used to identifyfeatures of the compressor 1100. Accordingly, a complete description ofthe exemplary embodiment of the compressor 1100 and the distractor 1000have been omitted, with only the notable differences being described.The compressor 1100 and the distractor 1000 include many of the featuresof the cap guide 400 while retaining their specific features that permitdistraction and compression between adjacent polyaxial bone screws 100,which are apparent to those having ordinary skill in the art, for thefunction of the compressor 1100 and the distractor 1000. Accordingly,although the cap guide instrument 400 is described in this applicationfor performing a number of functions during spine surgery, thecompressor 1100 and the distractor 1000 or other similar instruments maybe substituted therefore, when appropriate.

Referring to FIGS. 12-14, the distractor 1000 and the compressor 1100both include a ratchet arm 1017, 1117, a pivoting arm 1019, 1119 that ispivotally mounted to the cylindrical sleeve 1001, 1101 and a ratchetmechanism 1021, 1121 that can be used to lock the pivoting arm 1019,1119 relative to the cylindrical sleeve 1001, 1101 or mechanically movethe pivoting arm 1019, 1119 relative to the cylindrical sleeve 1001,1101. The distractor 1001 includes a blunt end portion 1019 a at thedistal end portion of the pivoting arm 1019 and the compressor 1100includes a hooked end portion 1119 a at the distal end portion of itspivoting end 1119. In use, the blunt end 1019 a of the distractor 1000abuts a side surface of the locking cap 700 of an adjacent polyaxialscrew 100 while the cylindrical sleeve 1001 is secured to the otherpolyaxial screw 100 and the screws 100 are urged away from each other,typically to relief pressure on nerves between two adjacent vertebrae V.In contrast, the hooked end portion 1119 a of the compressor 1100extends through the first and second slots 218 a, 218 b of the tissueretractor 200 opposite the screw 100 that the cylindrical sleeve 1101 isattached to. The hooked end 1119 a engages the locking cap 700 of thisscrew 100 and urges the polyaxial screws 100 and adjacent vertebrae Vtoward each other to compress the vertebrae V together or against aspacer S (FIG. 10C) positioned between the vertebrae V.

Referring to FIGS. 3-6B, 8 and 19A, the exemplary instrument set of thepresent application includes a scissor persuader 1400 having grooveengaging arms 1402 attached to a first hand grip 1460 a, a windowengaging nose 1404 secured to a second hand grip 1460 b and a releasetab 1406. When a polyaxial screw 100 has been inserted into thevertebrae V with the tissue retractor 200 mounted thereto, the rod R ispositioned in the rod slot 108 and the cap guide 400 with the lockingcap 700 secured at the distal end portion 402 of the cap guide 400 ispositioned in the partial pathway 206, the rod R may be difficult tofully seat in the rod saddle 101 a in certain situations. In addition,it may be difficult for the surgeon to urge the rod R far enough intothe rod slot 108 to initially engage the threads 712 of the threadedportion 702 with the threaded portions 114 of the arms 110 with onlyhand or manual force. The scissor persuader 1400 may be utilized toapply mechanical force to urge the cap guide 400 downwardly within thepartial pathway 206 of the tissue retractor 200 to urge the rod R intothe rod slot 108 and/or the threads 712 of the threaded portion 702 intoengagement with the threaded portions 114 of the arms 110.

In use, the groove engaging arms 1402 are positioned in the graspinggrooves 460 and the window engaging nose 1404 is engaged with a proximalend of the window 230 of the tissue retractor 200. The first and secondhandle grips 1460 a, 1460 b are squeezed together to urge the grooveengaging arms 1402 toward the window engaging nose 1404 and the capguide 400 further into the partial pathway 206 of the tissue retractor200. Urging the cap guide 400 downwardly causes the locking cap 700 tourge the rod R downwardly into the rod slot 108. The scissor persuader1400 may be utilized without blocking insertion of the drive shaft 504of the screwdriver 500 into the hollow cavity 406 and into engagementwith the drive feature 701 of the locking cap 700. In addition, thescissor persuader 1400 does not block engagement of the counter-torquehandle 600 with the cap guide 400. When the cap guide 400 has beenpersuaded to the assembled or working configuration relative to thetissue retractor 200, the persuader 1400 locks in position such that thesurgeon does not have to continue to hold the first and second handgrips 1460 a, 1460 b to maintain the position of the cap guide 400relative to the tissue retractor 200. To release the lock of the scissorpersuader 1400, the release tab 1406 is actuated and the scissorpersuader 1400 may be removed from engagement with the cap guide 400 andthe tissue retractor 200. The position of the clearance window 450 inalignment with the window 230 of the tissue retractor 200 providesclearance for the window engaging nose 1404 in operation.

Referring to FIGS. 1-8 and 19B, a threaded persuader 1500 may beutilized to similarly persuade the rod R into the rod slot 108,typically in situations where the travel of the scissor persuader 1400is insufficient to persuade the rod R. The threaded persuader 1500includes spring arms 1502 on opposing sides, a slider 1504 thatreleasably engages the locking cap 700 in a similar manner to theabove-described cap guide 400, a hand actuator 1506 at a proximal end ofthe threaded persuader 1500 to move the slider 1504 relative to thecylindrical sleeve 1501, anti-splay wings 1540 and an internal spline1508 to engage the spline 606 b of the counter-torque handle 600.

In use, if the rod R is positioned proud of the rod slot 108 asufficient distance that the scissor persuader 1400 is unable to engagethe cap guide 400 and the tissue retractor 200 to persuade the rod R orthe scissor persuader 1400 is unable to apply enough force to persuadethe rod R, the threaded persuader 1500 may be introduced into thepartial pathway 206 and engage the tissue retractor 200 proximate thedistal end portion 202 in a similar manner to the cap guide 400. Whenfully assembled and seated in the tissue retractor 200, the spring arms1502 spring outwardly into the windows 230 or a single window 230 of thetissue retractor 200 to translatably secure the threaded persuader 1500relative to the tissue retractor 200 and the polyaxial screw 100 alongthe longitudinal tissue retractor axis L-L. The hand actuator 1506 isrotated relative to the cylindrical sleeve 1501 such that the slider1504 moves downwardly toward the distal end and the saddle 704 engagesthe rod R. Further pivoting of the hand actuator 1506 urges the slider1504 further toward the distal end and persuades the rod R into the rodslot 108 and the threads 712 of the threaded portion 702 into engagementwith the threaded portions 114 of the arms 110. The urging forces ofpushing the rod R into the rod slot 108 are reacted through the tissueretractor 200 and into the cylindrical sleeve 1501 through the springarms 1502. When the rod R is persuaded a sufficient amount to allowengagement of the threads 712 of threaded portion 702 with the threadedportions 114 of the arms 110, the drive shaft 504 of the screwdriver 500is introduced through the hollow central channel 1510 of the threadedpersuader 1500 to screw the locking cap 700 into the body 102. To removethe threaded persuader 1500 from the tissue retractor 200, the springarms 1502 are urged inwardly out of the window 230 and the threadedpersuader 1500 slides out of the partial pathway 206.

Referring to FIGS. 1-5, 10A-10C, 13, 14, 16, 17 and 20, to remove thetissue retractors 200, 300 from the polyaxial bone screw 100 or anyother mechanism that engages the polyaxial bone screw 100 with a devicesimilar to the resilient movable arms 210 of the tissue retractors 200,300, the removal tool 1200 is utilized to actuate the resilientlymovable arms 210 from the relaxed position to the flexed position. Theremoval tool 1200 includes a cylindrical sleeve 1201, spring arms 1202,actuating arms 1204 with ramped distal surfaces 1206, a handle 1208 andanti-splay wings 1240.

In use, after the polyaxial screws 100 are inserted in the vertebra V,the locking caps 700 have been final tightened and the cap guide 400,counter torque handle 600, screwdriver 500 and other components havebeen removed from the partial pathway 206, the removal tool 1200 isinserted into the partial pathway 206. The cylindrical sleeve 1201 has adiameter slightly smaller than an inner diameter of the tissue retractor200 proximate the distal end portion 202. The cylindrical sleeve 1201slides into the partial pathway 206 until one of the spring arms 1202snap into the window 230, the window 330 or a related feature on otherinstruments of the exemplary instrument set to axially secure theremoval tool 1200 to the tissue retractors 200, 300. In this position,the actuating arms 1204 engage the retaining tab 216, 316 to urge theresiliently movable arms 210, 310 to the flexed position, wherein theattachment tab 212, 312 is moved out of engagement with the recess 116on the body 102. The ramped distal surfaces 1206 facilitate the flexingof the resilient movable arms 210, 310 outwardly to the flexed position.The anti-splay wings 1240, particularly with the first and second tissueretractors 300 a, 300 b, laterally retain the tissue retractors 200, 300relative to the cylindrical sleeve 1201. The removal tool 1200 and thetissue retractor 200, 300 or related instruments may then be removedfrom the patients body out of the generally conical incision CI andthrough the skin incision I.

The spring arms 1202 typically include a ramped nose 1202 a and arelatively squared or blunt butt end portion 1202 b. The ramped nose1202 facilitates engagement of at least one of the springs arms 1202 inthe window 230 of the tissue retractor 200 as the cylindrical sleeve1201 of the removal tool 1200 slides into the partial pathway 206. Theblunt butt end portion 1202 b is generally positioned against or near aproximal end of the window 230 to inhibit sliding movement of theremoval tool 1200 out of the partial pathway 206 once the spring arm1202 is engaged with the window 230. The spring arms 1202 operate in asimilar manner with respect to the windows 330 of the first and secondtissue retractors 300 a.

The windows 230, 330 may include a rough or uneven surface 230 a, 330 aproximate the windows 230, 330 on an outer surface of the bodies 201,301. The rough or uneven surface 230 a, 330 a proximate the windows 230,330 facilitate gripping and handling of the tissue retractors 200, 300by surgeons and technicians in an operating environment. For example,the rough or uneven surface 230 a, 330 a permits a surgeon, who may havewet and slimy gloves on their hands, to grip the rough or uneven surface230 a, 330 a with a thumb while urging the spring arm 1202 out of thewindow 230, 330 and sliding the removal tool 1200 out of the partialpathway 206, 306 of the tissue retractor 200, 300. The surgeon's wet andslimy finger may slip on the outer surface of the bodies 201, 301without inclusion of the rough or uneven surface 230 a, 330 a. The roughor uneven surface 230 a, 330 a may be comprised of grooves, knurling,cavities, spikes, surface roughenings or other like features.

Referring to FIGS. 1-5, 16, 17, 21A and 21B, a holder 1300 is utilizedto hold the polyaxial screw 100 and tissue retractors 200, 300 to drivethe polyaxial screws 100 into the vertebrae V. The holder 1300 includesa cylindrical sleeve 1301, a hollow retaining shaft 1302 with a threadeddistal end portion 1302 a, a holding sleeve 1304 at a proximal end and asafety shield 1306 that is slidable along an outside of the holdingsleeve 1304. The holding sleeve 1304 includes an anti-splay ring 1340 atits distal end to laterally retain the tissue retractors 200, 300 in anassembled configuration. The safety shield 1306 includes several springarms 1306 a that are selectively engageable with a first groove 1304 ain an actuating position (FIG. 21B) and a second groove (not shown) in asafety position (FIG. 21A) on the external surface of the holding sleeve1304. The holding sleeve 1304 also includes an actuating window 1304 cthat exposes an actuator 1302 a on an external surface of the retainingshaft 1302.

In use, the safety shield 1306 is moved to an actuating position whereinthe spring arms 1306 a engage the first groove 1304 a to secure thesafety shield 1306 in the actuating position. The threaded end portion1302 a of the retaining shaft 1302 is engaged with the internal threadedportion 114 of the arms 110 by manipulating the actuator 1302 a throughthe actuating window 1304 c, which is exposed when the safety shield1306 is in the actuating position. The tissue retractors 200, 300 areattached to the holder 1300 such that the proximal end portion 204 ispositioned under the anti-splay ring 1340. The polyaxial screw 100 andthe holder 1300 are guided to the surgical site through the generallyconical incision CI by a K-wire (not shown). When a tip of the bonescrew 104 contacts the vertebra V, the screwdriver 500 may be inserteddown the hollow retaining shaft 1302 to drive the polyaxial screw 100into the vertebra V. When the screwdriver 500 is driving the screw 104into the vertebra V, the safety shield 306 is moved to the safetyposition covering the actuating window 1304 c and the actuator 1302 a toprevent a surgeon from moving the actuator 1302 a and disengaging theretaining shaft 1302 from the polyaxial pedicle screw 100. The surgeongrasps the holder 1300 at the safety shield 1306 and the holding sleeve1304 and drive the polyaxial screw 100 into the vertebra V. The safetyshield 1306 is then moved from the safety position to the actuatingposition, where the spring arms 1306 a engage the first groove 1304 a toretain the safety shield 1306 in the safety position. The actuator 1302a is manipulated to rotate the retaining shaft 1302 and disengage thedistal threads 1302 a from the internal threaded portions 114 of thearms 110. The holder 1300 is removed from the generally conical incisionCI leaving the polyaxial screw 100 and tissue retractors 200, 300 in thegenerally cylindrical incision CI.

Referring to FIGS. 6A, 6B, 12 and 22, the exemplary instrument set alsoincludes a cap tray 1600 for storage and staging of the locking caps700. The cap tray 1600 of the exemplary embodiment includes six capstations 1602 that each receive an individual locking cap 700. The captray 1600 is not limited to the inclusion of six cap stations 1602 andmay include nearly any number of cap stations 1602 that is desired bythe use for storing a desired number of locking caps 700. Each of thecap stations 1602 includes a centrally located pedestal 1604 with anarcuate top surface that mates with the actuate surface 704 a of thesaddle portion 704, four alignment ribs 1606 and two button grooves1608. The alignment ribs 1606 cooperate with the blocking tabs 408 andthe arm 422 to align the arms 706, 708 of the saddle 704 generallyperpendicular to the indicias 432 such that the saddle 704 is aligned toengage the rod R when the cap guide 400 is positioned in the partialpathway 206. The button groove 1608 receives the guide button 426 of thecap guide 400 to ensure alignment of the saddle 704 with the cap guide400 for receipt of the rod R.

In use, the cap guide 400 or any other instrument of the exemplaryinstrument set, including the distractor 1000 or compressor 1101 thatreceive and retain the locking caps 700 therein, may stab and grab thelocking caps 700 directly from the cap tray 1600. Specifically, the usergrasp the cap guide 400 and stabs the locking cap 700 that is positionedin one of the cap stations 1602. The features at the distal end of thecap guide 400 cooperate with the features in the individual cap station1602 to align and properly position the locking caps 700 at the distalend portion 402 of the cap guide 400. The cap tab 414 engages thethreads 712 of the locking cap 700 to coaxially align the locking cap700 with the hollow cavity 406. Therefore, when the cap guide 400 with alocking cap 700 secured in the distal end is introduced into the partialpathway 206 and the saddle 704 engages the rod R, the saddle 704 ispre-oriented to engage the rod R and the threads 712 are pre-oriented toengage the threaded portions 114 of the arms 110. Such a configurationmay ease insertion of the locking cap 700 onto the body 102 anddiminishes any possibility that the threads 712 of the locking cap 700cross-thread with the threaded portions 114 of the arms 110, due to thepre-orientation of the locking cap 700 relative to the body 102.

Referring to FIGS. 1-22, in use, the polyaxial bone screw 100 is coupledto the tissue retractor 200 by sliding the distal end portion 202 of thetissue retractor 200 over the body 102 until the attachment tabs 212mate with the corresponding recesses 116 of the body 102. Lower ordistal surfaces of the attachment tabs 212 are tapered in a ramp-likeconfiguration such that the top edge of the arms 110 urge the attachmenttabs 212 from the relaxed position to the flexed position to allow theattachment tabs 212 to move over and past the locking edge 117 into therecesses 116. The polyaxial bone screw 100 is fixed to a vertebra V of apatient (FIG. 21), typically guided by the K-wire. The polyaxial pediclescrews 100 and the tissue retractors 200, 300 are inserted into thegenerally conical incision CI using the holder 1300, as was describedabove. Adjacent tissue retractors 200 move to the nested configuration(FIG. 10B) under the urging of the surgeon and the patient's soft tissueT. A portion of the rod R is inserted through the tissue retractor 200until the rod R is seated in the rod receiving portion 112 of thepolyaxial bone screw 100.

The locking cap 700 is positioned within one of the cap stations 1602 ofthe cap tray 1600 such that the saddle portion 704 is in an alignedconfiguration with respect to the tray 1600. The distal end portion 402of the cap guide 400 is placed over the locking cap 700 in the tray 1600to receive the locking cap 700. By virtue of the locking cap 700 havingbeen previously aligned within the tray 1600, the saddle portion 704 ofthe locking cap 700 is aligned within the cap guide 400 when the capguide 400 receives the locking cap 700 from the tray 800. That is, thearms 706, 708 of the locking cap 700 align with the slots 410 in the capguide 400. The locking cap 700 is inserted through the tissue retractor200 using the cap guide 400 until the cavity 710 in the saddle portion704 of the locking cap 700 mates with the rod R and the threaded portion702 thereof is received by the threaded portions 114 of the body 102 ofthe polyaxial bone screw 100.

As is described above, the locking cap 700 is aligned with andpositioned for engagement within the partial pathway 206 of the tissueretractor 200 without ever coming into contact with the screwdriver 500.Although the screwdriver 500 generally includes a self-retaining featurewhen engaged to the locking cap 700, such a feature is typically lessstable than the above-described engagement between the locking cap 700and the cap guide 400. Specifically, when the cap guide 400 is movingdownwardly through the partial pathway 206, the locking cap 700 isgenerally surrounded and protected from disengagement forces by thedistal end portion 402 of the cap guide 400. Therefore, risk of thelocking cap 700 disengaging from the cap guide 400 during insertionthrough the partial pathways 206 of the tissue retractors 200 in theassembled and implanted positions is less likely than situations wherethe locking cap 700 is self-retained by the screwdriver 500, insertedthrough the generally conical incision CI and into engagement with thebody 102. Disengagement of the locking cap 700 from any instrument whilein the conical incision CI is unfavorable as the locking cap 700 must beretrieved through the minimally invasive, generally conical incision CI.The engagement of the locking cap 700 with the distractor 1000, thecompressor 1100, the threaded persuader 1500 or other similarinstruments provides similar retaining protections to the locking cap700.

Generally, concurrently with the locking cap 700 being received by thebody 102, the cap guide 400 is coupled to the tissue retractor 200 torotatably fix the tissue retractor 200 to the cap guide 400 by matingthe blocking ribs 228 of the tissue retractor 200 with the correspondingblocking tabs 408 of the cap guide 400. The drive shaft 504 is theninserted into the hollow cavity 406 of the cap guide 400 to mate withthe locking cap 700. The surgeon can now perform initial tightening ofthe locking cap 700 within the body 102 to at least provisionally securethe rod R to the polyaxial screw assembly 100.

Once the locking cap 700 is provisionally tightened, any manipulation ofthe position of the polyaxial bone screw 100 with respect to the rod R,such as compression or distraction with another polyaxial bone screw100, can be performed without removing the drive shaft 504 from thehollow cavity 406 of the cap guide 400, assuming the locking cap 700 isinserted utilizing the distractor 1000 or compressor 1100, respectively.The counter-torque handle 600 is coupled to the cap guide 400 byinserting the drive shaft 504 into the open-ended slot 610 of thecounter-torque handle 600 and inserting the instrument interface 606into the hollow cavity 406 of the cap guide 400, typically by mating thesplines 608 b of the counter-torque handle 600 with the complementarysplines 412 of the cap guide 400. In this configuration, the drive shaft504 is rotatable within the counter-torque handle 600. Final tighteningof the locking cap 700 is performed, such that the locking cap 700 bearsagainst the rod R, by rotating the drive shaft 504. The rod R isthereafter fixed with respect to the polyaxial bone screw 100 and thetorque input to the polyaxial pedicle screw assembly 100 by thescrewdriver 500 is reacted through the body 102, the bulked-up portion203 of the tissue retractor 200 between the blocking ribs 228 and thescrew engagement ribs 214, the stiff and strong sleeve 401 of the capguide 400 and the counter-torque handle 600. Accordingly, the relativelythin body 201 of the tissue retractor 200 and the arms 110 do not reactsignificant portions of the final tightening forces and only react theforces over short distances adjacent the top end of the arms 110.

It will be appreciated by those skilled in the art that changes could bemade to the exemplary embodiment described above without departing fromthe broad concept thereof. It is understood, therefore, that thedescribed device and method are not limited to the particular embodimentdisclosed, but it are intended to cover modifications within the spiritand scope of the exemplary embodiment as defined by the appended claims.

1. (canceled)
 2. A system for use in minimally invasive spine surgery,the system comprising: a bone anchor having first and second arms thatare spaced from one another along a first direction so as to define arod-receiving channel between the first and second arms; and a tissueretractor that extends from one of the first and second arms but not theother of the second arms along a second direction that is perpendicularto the first direction, the tissue retractor defining a concave innersurface that defines a partial pathway.
 3. The system of claim 2,wherein the bone anchor defines a plane that extends between the firstand second arms, and the tissue retractor is disposed entirely on oneside of the plane.
 4. The system of claim 2, wherein the tissueretractor includes a resiliently movable arm that is movable between anengaged position and a flexed position, and the resiliently movable armextends from one of the first and second arms of the bone anchor.
 5. Thesystem of claim 2, comprising a second tissue retractor that extendsanother one of the first and second arms but not the other of the firstand second arms, the second tissue retractor defining a second innersurface that defines a partial pathway
 6. The system of claim 5, furthercomprising a rod sized to be inserted between the first and secondtissue retractors and into the rod-receiving channel of the bone anchoralong the second direction, such that the rod is elongate along a thirddirection that is perpendicular to both the first and second directions.7. The system of claim 2, further comprising: an instrument configuredto move at least one of the first bone anchor and a second bone anchorimplanted in a second vertebra relative to one another, the instrumentcomprising: a sleeve having a distal sleeve end configured to removeablycouple to the tissue retractor, and a proximal sleeve end spaced fromthe distal end, the sleeve defining a hollow cavity that extends betweenthe proximal and distal ends of the sleeve, and the sleeve configured tobe removably couplable to the tissue retractor within the partialpathway; a pivoting arm that is pivotally mounted to the sleeve; and aratchet mechanism configured to move the pivoting arm relative to thesleeve so as to cause at least one of the first and second bone anchorsto move relative to the other of the first and second bone anchors. 8.The system of claim 7, wherein the tissue retractor comprises at leastone resiliently movable arm configured to engage a bone anchor so as tocouple the tissue retractor to the bone anchor, and the sleeve definesat least one slot at the distal sleeve end portion, wherein each of theat least one slot is aligned with one of the at least one resilientlymovable arms.
 9. The system of claim 7, wherein the proximal sleeve endis configured to engage a counter-torque handle such that the sleeve andcounter-torque handle are rotatably fixed relative to one another. 10.The system of claim 7, wherein the instrument is a distractor that isconfigured to move the pivoting arm relative to the sleeve so as tocause at least one of the first and second bone anchors to move awayfrom the other of the at least one of the first and second bone anchors.11. The system of claim 10, wherein a distal end of the pivoting armincludes a blunt end portion configured to engage the second boneanchor.
 12. The system of claim 7, wherein the instrument is acompressor that is configured to move the pivoting arm relative to thesleeve so as to cause at least one of the first and second bone anchorsto move towards the other of the at least one of the first and secondbone anchors.
 13. A method comprising: driving a bone anchor into bone,the bone anchor having first and second arms that are spaced from oneanother along a first direction so as to define a rod-receiving channelbetween the first and second arms, wherein a tissue retractor extendsfrom one of the first and second arms but not the other of the first andsecond arms, such that an inner surface of the tissue retractor definesa partial pathway, wherein the inner surface is concave.
 14. The methodof claim 13, wherein a second tissue retractor extends from the other ofthe first and second arms, but not the one of the first and second arms,such that an inner surface of the second tissue retractor defines arespective partial pathway.
 15. The method of claim 14, comprising thestep of inserting a rod between the first and second tissue retractorsand into the rod-receiving channel of the bone anchor along a seconddirection, perpendicular to the first direction such that the rod iselongate along a third direction, perpendicular to both the first andsecond directions.